Ant symbioses: colony-level effects of antagonistic and mutualistic interactions in two model ant systems
Abstract
An ant colony can be considered a superorganism with the workers analogous
to cells and the entire colony analogous to an organism. Few studies have taken a
colony-level approach to understanding how ant societies function. This dissertation
explores how ant colonies respond and adjust to changes in the environment brought
about through symbiotic relationships. First, I focus on the antagonistic interaction
between a specialized phorid fly parasitoid and its host, the red imported fire ant,
Solenopsis invicta. Phorid flies, which inject their eggs into fire ant workers, have
recently been introduced into the United States as a biological control agent of this
invasive pest, but the impact of these flies on fire ant populations is yet unknown. I
examine how phorids affect colony growth, foraging efficiency, and caste recruitment
of S. invicta. This study is the first to link indirect (behavioral modification of
foraging) and direct (mortality to workers) effects of parasitic flies on fire ants.
Second, I focus on the mutualistic interaction between ant farmers and their cultivated
fungi. An intriguing dimension of complexity in the attine ant-fungus mutualism
derives from potential conflict over the sex ratio, i.e., the ratio of male to female
reproductives produced by a social insect colony. In hymenopteran societies, conflict
over sex ratios is presumed to exist between the mother queen and her daughters
(workers) due to differences in their genetic relatedness to the sexuals. The presence
of heterospecific symbionts in a social insect colony (e.g., fungus-growing ants)
complicates predictions of conflict resolution even furthermore. Three parties are
potentially in conflict over sex ratios: the mutualistic fungus, the workers, and the
queen. I studied the dynamics of sex-ratio conflict and ant-fungus cooperation in the
primitive attine, Cyphomyrmex muelleri. I show that ants and native cultivars have
coevolved to enhance mutualistic interactions. Despite these cooperative interactions,
ant-cultivar conflict may have been revealed by the effect of cultivar switches on ant
sex ratio and male survival. In sum, this work demonstrates that the integration of
colony-level and individual-level investigations provides a comprehensive
understanding of how ant societies (superorganisms) function and respond to their
symbiotic partners.
Department
Description
text